Fiber Orientation,Warpage Deformation And Mechanical Properties Of Combining In-Mold Decoration And Fiber-Reinforced Injection Molding

Injection molding technology is the most widely used manufacturing method for molding fiber reinforced composites at present.Compared with traditional injection molding,fiber-reinforced injection molding(FRIM)has improved the mechanical properties of parts to some extent because of the existence of reinforced fibers.However,in the molding process,the surface of the product is prone to the phenomenon of"floating fiber",which seriously affects the apparent quality and service performance of the product.In order to solve this problem,a new method that combined in-mold decoration and fiber-reinforced injection molding(IMD/FRIM)was proposed,which attempts to fabricate fiber-reinforced polymer products that cover the"floating fiber"by embedding the film in the mold cavity and bonding it tightly with the fiber-reinforced polymer melt.However,the unbalanced temperature field after film covering will cause the unbalanced distribution of fiber orientation,leading to the deterioration of service performance of the product.Therefore,the fiber orientation,warpage deformation and mechanical properties under the new molding process are studied in this paper.The main contents are as follows:(1)The flow governing equation of IMD/FRIM is established.Based on the theory of polymer rheology and heat transfer,the flow governing equation of IMD/FRIM is established,and combined with the melt viscosity and fiber orientation model,the computational model and theoretical basis are provided for the subsequent numerical simulation,and the physical experiments needed in this paper are introduced.(2)The fiber orientation of IMD/FRIM and its influence on warpage and mechanical properties are studied.Taking tensile spline as the research object,FRIM and IMD/FRIM are compared and analyzed by combining numerical simulation with physical experiment.The results show that compared with FRIM,the fiber orientation distribution of IMD/FRIM is uneven and the degree of fiber orientation is lower.The change trend of tensile modulus and shear modulus of the two processes is consistent with the corresponding fiber orientation change trend.The tensile strength of IMD/FRIM part is lower,but the bending strength and shear strength are higher.The orderly arrangement of fiber orientation can reduce the warping deformation,but the film will aggravate the warpage deformation,which is 124.21%increased than FRIM part.(3)The influence of parameters on the fiber orientation,warpage deformation and mechanical properties of IMD/FRIM is studied.Based on numerical simulation platform,the main process parameters are analyzed by single factor method,including melt temperature,mold temperature,injection rate,holding pressure and holding time,on fiber orientation and properties.The results show that the mold temperature has the greatest effect on fiber orientation,while the holding pressure has the least effect on fiber orientation.Holding pressure has the greatest effect on warpage deformation,while injection rate has the least effect on warpage deformation.The mold temperature has the greatest influence on the tensile modulus,while the melt temperature has the least influence on the tensile modulus.When the single process parameters are 245°C of the melt temperature,20°C of the mold temperature,10 cm~3/s of the injection rate,100 MPa of the holding pressure and 12 s of the holding time,the fiber orientation,warpage and tensile properties of the product are the best.(4)In order to solve the problems of uneven distribution of fiber orientation and large warpage caused by unbalanced temperature field in single-sided in-mold decoration combined with fiber-reinforced injection molding(S-IMD/FRIM),an innovative method is proposed by utilizing double-sided in-mold decoration combined with fiber-reinforced injection molding(D-IMD/FRIM).Through numerical simulation and experiment,the melt temperature,viscosity,fiber orientation and properties of S-IMD/FRIM and D-IMD/FRIM are compared.The results show that the melt temperature,viscosity and fiber orientation distribution of D-IMD/FRIM are more uniform than those of S-IMD/FRIM.The degree of fiber orientation and tensile strength of D-IMD/FRIM parts are slightly lower,while the bending strength and shear strength are slightly bigger,and the warpage deformation is reduced by 47.66%.